On 18 August 2012 11:41, Brendan Fennell <bfennell@skynet.ie> wrote:
>>> On Sat, 18 Aug 2012, Peter Maydell wrote:>>> On 18 August 2012 03:55, Brendan Fennell <bfennell@skynet.ie> wrote:>>>>>> Signed-off-by: Brendan Fennell <bfennell@skynet.ie>>>> --->>> hw/pl190.c | 2 +->>> 1 files changed, 1 insertions(+), 1 deletions(-)>>>>>> diff --git a/hw/pl190.c b/hw/pl190.c>>> index cb50afb..d69d5be 100644>>> --- a/hw/pl190.c>>> +++ b/hw/pl190.c>>> @@ -133,7 +133,7 @@ static uint64_t pl190_read(void *opaque,>>> target_phys_addr_t offset,>>> s->priority = i;>>> pl190_update(s);>>> }>>> - return s->vect_addr[s->priority];>>> + return s->vect_addr[s->priority - 1];>>> case 13: /* DEFVECTADDR */>>> return s->vect_addr[16];>>> default:>>>>>> This doesn't look right -- if s->priority is zero then we'll read off>> the beginning of the array.>> What's the actual bug you're trying to fix here?>>> The bug is that when, for example, interrupt 4 triggers the VECTADDR of> interrupt 5 is returned by pl190_read().>> Each s->prio_mask entry contains the interrupt mask for all *higher*> priority interrupts, see pl190_update_vectors(). This means that> s->prio_mask[0] is always zero (as zero is the highest priority),> s->priority can never be zero as ((s->level | s->soft_level) &> s->prio_mask[0]) is always zero.>> Therefore after the for loop in pl190_read() i is the index of the> current highest priority interrupt + 1.
Yes, looking more closely, you're right (though that's not obvious
at all...)
But we set s->priority to i, which seems wrong -- s->priority should
be the priority of the current active interrupt, and that's how we
treat it in pl190_update() [we assert s->irq if there's a pending
interrupt that's higher priority than the one we're currently servicing.]
So I think the fix ought to be to change the s->prio_mask[i] in the
loop to be s->prio_mask[i+1] instead. Then we'll exit the loop with
i as the current highest priority interrupt, which is what the following
code expects.
Some sort of explanatory comment in the loop might also assist
future readers :-)
-- PMM